1. 1
4 2
3
Effect of Burn-up and High
Burn-up Structure on UO2
Spent Fuel Matrix Dissolution
D. Serrano-Purroy1, I. Casas2, E. González-Robles3,
J. P. Glatz1, D. Wegen1, F. Clarens3, J. Giménez2,
J. de Pablo2,3, A. Martínez-Esparza4
MRS’11, BUENOS AIRES, OCTOBER 2-6, 2011

2. This work is a part of a Collaboration
Agreement between ITU/JRC-ENRESA-
CTM/UPC to obtain the scientific data
needed to better understanding the
behaviour of High Burn-up Spent Fuels

3. SPENT FUEL DISSOLUTION
-2
log Fractional Release Rate (d-1)
-3
-4
-5
grain boundaries
UO2-matrix
Rod Actínides & FP -6
14C (~ 98 %)
Gap matrix
14C; 129I;
135Cs; 137Cs; -7
79Se; 99Tc;
90Sr
gap
Cracks -8
Grain Boundary
14C; 129I; 0 1 2 3 4 5 6 7
Bubbles
135Cs; 137Cs;
79Se; 99Tc; 90Sr log time (y)
L.H. Johnson, D.W. Shoesmith, “Radioactive Waste Forms
for the future“, W. Lutze and R.C. Ewing, Eds., 1988

4. PREVIOUS UO2-MATRIX DISSOLUTION RATES
• Dynamic experiments -9.00
• Air conditions
• Powder -9.50 Gray_33 MW d/ kgU
• Fragment
• Segment (Fuel+Cladding) Serrano_53 MW d/ kg U
-10.00
log r (mol/m2·s) Röllin_43 MW d/ kgU
-10.50 Gray_28 MW d/ kgU (0.01 M
HCl/DIW)
Gray_43 MW d/ kgU (0.01M
HCl/DIW)
-11.00
Serrano_53 MW d/ kgU_segment
Serrano_29 MW d/ kg U_segment
-11.50
Jegou_60 MW d/kg U_segment
-12.00
-6 -5 -4 -3 -2 -1
log [HCO3-]

5. High Burn-up Structure (HBS)
Increasing burn-ups, neutron capture of U-238 produces Pu-239 generating
an external layer with a higher burn-up (BU), increased porosity and fuel
grain subdivision resulting on the formation of the so-called HBS. The width
of this layer, observed for BU’s higher than 40 MW d/kgU, increases with
the BU and depends on the irradiation history.
Intermediate zone HBS
HBS particle
CORE particle

6. RIM THICKNESS
110
100
90
Rt = 5.44BUR – 281
Rim BU (MW/ d kgU)
80
70
60
50
40
30
20
20 30 40 50 60 70 80
Average BU (MW/d kgU)
Johnson L., Ferry C., Poinssot C., Lovera P. Estimates of the Instant
Release Fraction for UO2 and MOX Fuel at t=0. NAGRA-TR-04-08, 2004

7. RN release from Spent Fuel
Grain boundaries:
C, I, S, Cs, Se, Tc
Grains:
Gap region : (U,An,Ln)O 2
C, I, Cs, Se, Tc Oxide precipitates:
Rb, Cs, Ba, Zr, Nb, Mo, Tc
?-particles/ metallic precipitates
Mo, Ru, Pd, Tc, Rh
20kV x 1.500 µm 030996
10
(Ag, Cd, In, Sn, Sb)
Cracks
Fission Gas bubbles: RIM or HBS:
Xe, Kr, I enriched in Pu
Pellet gap
Cladding : C

8. Objective
 Study the leaching behavior of High Burn-up
PWR fuels (48 and 60 Mw d/kgU) with
special emphasis on the HBS region related
to UO2-matrix dissolution

9. Spent fuel samples
Burn-up 48 60
(MW d/kgU) (MBU) PWR (HBU) PWR
MBU
Irradiation cycles 3 5
End of radiation 2000 2001
RIM (µm)
76 µm 155 µm
calculated
HBU

10. Spent fuel sample preparation
Two different samples were prepared from a different radial position in order to study the
effect of HBS region
1. Cut pin into segments
2. Drill
Core sample
3. Separation from cladding
RIM width
OUT sample OUT sample
4. Sieving (50-100 µm)
5. Removing fines

11. Spent fuel sample preparation
HBU: Core (left) and OUT (right) sample after drilling and detachment

12. Spent fuel sample preparation
SEM characterisation of core sample a) before cleaning b)
after cleaning at 1000 magnification (Scale: 30 µm)

13. Spent fuel sample characterization
Fuel Parameter Core OUT
Mean particle
68 ± 15 82 ± 8
size (μm)
60BU
Specific surface
0.027 ± 0.007 0.022 ± 0.002
area (m2/g)
Mean particle A: 45 ± 15
90 ± 40
size (μm) B: 140 ± 50
48BU
Specific surface A: 0.04 ± 0.01
0.020 ± 0.009
area (m2/g) B: 0.013 ± 0.009

14. Spent fuel sample characterization
 The percentage of the surface broke through trans-
granular process in the Core sample was 98 % for
48MBU fuel and 97% for 60HBU fuel. Therefore, only
about 3% of the particle surface was estimated to
contain open grain-boundaries in both fuels.
 The percentage of HBS particles present in OUT
samples for 48MBU and 60HBU fuels determined by
direct counting from SEM images is 5 and 19
respectively, these values change to 19 and 40 if
geometry is taking into account.

15. Experimental Setup

16. Experimental Setup installed inside Hot Cell

17. Inventory for CORE, OUT (μg of element/g of SNF)
Element 60BU-CORE 60BU-OUT 48BU-CORE 48BU-OUT
Rb 500 ± 10 600 ± 100 320 ± 20 490 ± 20
Sr 800 ± 40 800 ± 100 730 ± 100 700 ± 20
Y 650 ± 10 770 ± 30 540 ± 10 660 ± 30
Inventory of each fraction
Zr 6300 ± 200 7900 ± 700 3800 ± 300 4500 ± 200
experimentally Mo 5900 ± 300 8000 ± 400 3600 ± 200 4500 ± 200
Tc 1300 ± 100 1600 ± 50 840 ± 30 1090 ± 30
determined by dissolution
Ru 4400 ± 200 5300 ± 600 2400 ± 100 3200 ± 200
in acidic media and Rh 650 ± 20 800 ± 100 510 ± 20 700 ± 100
further HR-ICP-MS and Cs 3800 ± 200 4800 ± 400 2600 ± 200 4200 ± 100
Ba 3300 ± 400 4300 ± 500 1800 ± 400 2000 ± 300
γ-spectroscopy analysis La 2000 ± 400 2300 ± 300 2700 ± 1000 2800 ± 500
Ce 4100 ± 500 4500 ± 800 3000 ± 700 3000 ± 400
Pr 1800 ± 200 2100 ± 300 1300 ± 200 1100 ± 200
Nd 7000 ± 1000 8000 ± 900 4900 ± 1300 4000 ± 600
Sm 1270 ± 100 1500 ± 100 1000 ± 200 800 ± 100
Eu 190 ± 10 200 ± 20 130 ± 10 130 ± 10
Gd 620 ± 20 800 ± 200 340 ± 40 300 ± 30
U 780000 ± 10000 770000 ± 60000 790000 ± 10000 780000 ± 10000
Np 810 ± 80 760 ± 80 900 ± 100 750 ± 20
Pu 8000 ± 540 11000 ± 1600 10400 ± 600 15200 ± 400
Am 840 ± 100 1200 ± 100 500 ± 30 800 ± 30
Cm 290 ± 40 460 ± 50 70 ± 10 110 ± 10

18. Experimental conditions
•NaHCO3 10-3 mol·dm-3
•NaCl 1.9·10-2 mol·dm-3
•In air PO2 21%
•Temperature 25 ± 5 ºC
•pHi 8.0 ± 0.2
•pHo 7.2 ± 0.5
•Flow rate 0.025-0.1 L/min
•Weight of solid 1g

19. Dissolution Rates:
Q Ci
rate i
A
Radionuclide rates normalized to uranium:
massU Mi
normalized ratei ratei
massi MU

20. 60HBU Dissolution & normalized rates for Actinides
CORE CORE
1,E-07 1,E-08
1,E-08
1,E-09 1,E-09
norm. rates (mol/m 2. s)
1,E-10
rates (mol/m 2. s)
1,E-11 1,E-10
1,E-12
1,E-13 1,E-11
1,E-14
1,E-15 1,E-12
1,E-16
1,E-17 1,E-13
0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500
time (d) time (d)
U Np Pu Am Cm U Np Pu Am Cm
OUT OUT
1,E-07
1,E-08
1,E-09 1,E-08
rates (mol/m 2.s)
1,E-10
norm. rates (mol/m s)
2.
1,E-11 1,E-09
1,E-12
1,E-10
1,E-13
1,E-14
1,E-11
1,E-15
1,E-16 1,E-12
0 100 200 300 400 500
1,E-13
tim e (d)
0 100 200 300 400 500
time (d)
U Np Pu Am Cm
U Np Pu Am Cm

21. 48 MBU Dissolution & normalized rates for Actinides
CORE
1.E-08
1.E-09
1.E-10
rates (mol m-2 s-1)
1.E-11
1.E-12
1.E-13
1.E-14
1.E-15
0 50 100 150 200 250 300 350
time (d)
U Np Pu Am Cm
OUT OUT
1.E-06 1.E-06
1.E-07
1.E-07
1.E-08 normalised rates (mol m s-1)
-2
1.E-08
rates (mol m s-1)
1.E-09
-2
1.E-10
1.E-09
1.E-11
1.E-12 1.E-10
1.E-13
1.E-11
1.E-14
1.E-15 1.E-12
0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350
time (d) Time (days)
U Np Pu Am Cm U Np Pu Am Cm

22. Results
CORE OUT CORE OUT
60HBU 60HBU 48MBU 48MBU
NORMALIZED
RATE
(mol/m2 s)
U 5.1 10-12 2.1 10-12 8.0 10-11 4.0 10-11
Np 1.6 10-10 5.2 10-11 1.0 10-10 8.0 10-11
Pu 1.0 10-11 5.7 10-12 3.0 10-11 1.4 10-11
Am 3.5 10-12 2.5 10-12 5.0 10-11 2.0 10-11
RATIO
Np/U 11.3 15.2 1.4 2.2
Pu/U 1.2 1.7 0.4 0.4
Am/U 0.4 0.6 0.7 0.7

23. Some remarks
 Uranium and Actinide dissolution rates are twice
faster in the CORE region than in the Periphery
 Except for Np in 60HBU fuel, actinides dissolve
congruently with uranium
 Uranium dissolution rate is lower in 60HBU fuel than
in 48MBU fuel

24. 60HBU Normalized Rates for Fission Products
CORE OUT
1,E-07 1,E-07
normalized rates (mol/m 2.s)
1,E-08 1,E-08
normalized rates (mol/m2.s)
1,E-09 1,E-09
1,E-10
1,E-10
1,E-11
1,E-11
1,E-12
1,E-12
1,E-13
1,E-13
1,E-14
1,E-14
0 100 200 300 400 500 0 100 200 300 400 500
time (d) time (d)
Rb Sr Y Zr Mo Tc Ru Rh Cs Nd U Rb Sr Y Zr Mo Tc Ru Rh Cs Nd U

25. 48MBU Normalized Rates for Fission Products
CORE OUT
1.E-07 1.E-06
1.E-07
normalised rates (mol m-2 s-1)
1.E-08
normalised rates (mol m-2 s-1)
1.E-08
1.E-09
1.E-09
1.E-10
1.E-10
1.E-11 1.E-11
1.E-12 1.E-12
1.E-13
1.E-13 0 50 100 150 200 250 300 350
0 50 100 150 200 250 300 350
times (t)
time (d)
Rb Sr Y Zr Mo Tc Ru Rh Cs La Nd U Rb Sr Y Zr Mo Tc Ru Rh Cs La Nd U

26. Results
Ratio CORE OUT CORE OUT
60HBU 60HBU 48MBU 48MBU
Rb/U 25.4 113.7 11.0 4.0
Sr/U 7.7 16.2 3.5 1.4
Y/U 1.8 1.7 2.3 3.0
Zr/U 0.02 0.04 0.2 0.1
Mo/U 4.1 29.7 4.2 2.0
Tc/U 0.5 0.5 1.3 1.1
Ru/U 0.3 0.8 0.3 0.7
Rh/U 0.2 0.5 0.3 0.8
Cs/U 2.0 40.2 10.0 3.1

27. Results: FP rates/ U rate
120,00
100,00
80,00
dissolution rate ratio
60core
60,00 60out
48core
48out
40,00
20,00
0,00
Rb/U Sr/U Y/U Zr/U Mo/U Tc/U Ru/U Rh/U Cs/U

28. Some remarks
 Fission products normalized dissolution rates are
similar in 48MBU for both core and out samples
 Fission products normalized dissolution rates are
higher in out than in core samples in 60HBU
 Rb, Sr, Mo, Cs are more segregated from UO2-grains
in 60HBU than in 48MBU

29. Matrix dissolution rate comparison
-9.00
Gray_33 MW d/kgU Röllin_43 MW d/kg U this_work_6OHBU_out this_work_60HBU_core
Serrano_53 MW d/kg U this_work_48MBU_core this_work_48MBU_out
-9.50
-10.00
log rate
-10.50
-11.00
-11.50
-12.00
-4.50 -4.00 -3.50 -3.00 -2.50 -2.00 -1.50 -1.00
log [HCO3-]

30. Conclusions
-phase Dissolution lower
UO2-matrix dissolution rate than UO2-matrix
Grains similar in both HBU
higher in MBU than in HBU Grains
and MBU fuels
Gap Rim Boundaries
IRF
2 options:
Not studied in this  IRF or 2 options Congruent dissolution
 matrix  IRF or with UO2-matrix:
work, no gap was  matrix
present Np, Pu, Am, Cm, excep
t for Np in 60HBU.
This work indicates that High BU Rb, Sr, Cs, Mo are
Structure (RIM) can not be more segregated from
considered IRF. OUT Dissolution UO2-grains in 60HBU
rate (including a percentage of RIM) than in 48MBU
lower than CORE rate for both HBU
and MBU Not studied in detail in
this work, only 3% of
grain boundary present

31. THANK YOU FOR YOUR ATTENTION
GRACIAS POR SU ATENCIÓN
And thanks to Argentina for sending
this guy to Barcelona
Que bueno que viniste